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shagone 13th July 2007 09:33 PM

sony xm-754hx problem
i am having problems with a sony xm-754hx 4 channel amp. at first it faulted out for over current and i replace one channels pair of output fets that were shorted (irf540 and irf950 with irf540n and irf9540n.)

what is the "n" for? was this swap ok?

now the amp draws 20 amps of current upon power up with no audio signal going to it but the over current light is not on any more. strange?

i suspected the power supply fets because they read almost shorted from gate to source on all 4 of the fkv550's.

when i pulled them they all tested fine on their own but the meter still beeped constantly from the pads where the gate and source would be on the board.

i looked for any bad solder joints or charred components but everything looks fine.

what could this be? what else should i check?

Thanks in advance for any suggestions.

1moreamp 14th July 2007 05:07 AM

Sounds like the fet gate drivers are toast Maybe... The channels could still be blown in front of the fets you replaced and if so your turning the amp on into a over drive condition that would draw 10 or more amps.

I would remove the outputs and retest the amp for idle current. and then take voltage readings at the gate for the output fets to see what kind of drive signal they are getting.

Good luck :)

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